The present invention relates to automatic fire sprinklers, and more particularly, to an automatic fire sprinkler having a safety mechanism for preventing accidental or malicious activation of the sprinkler, and averting the water damages associated therewith.
An automatic fire sprinkler typically includes a body having a base, an inlet connected to a source of pressurized water (or fire-retardant fluid), and an outlet, both defined by the base, a passageway between the inlet and outlet, and a flow-adjusting orifice, usually located upstream close to the outlet. Additionally, a plug closing the outlet when the sprinkler is in standby condition is held in place by a thermally sensitive element (also known as a fuse). When the temperature is elevated to a pre-determined value, the thermally sensitive element disintegrates. Consequently, the water pressure urges the plug away from the outlet, enabling the sprinkler to discharge. A supported deflector, integrally connected to the body, distributes the water stream flowing from the outlet, so as to disperse the stream over the region to be protected by the sprinkler.
Generally, the thermally sensitive element is a special glass tube containing an expansive liquid, such that at a pre-determined elevated temperature, the glass is broken by the pressure of the expansive liquor. Alternatively, the thermally sensitive element is fabricated from soft metal solder, which softens or melts at the pre-determined temperature, thus permitting the sprinkler to discharge. As a result of these weak materials of construction, the thermally sensitive elements are vulnerable and may easily be accidentally damaged and activated. Accidental activation of fire sprinklers in fire-protected areas may occur during various operations normally carried in these areas, such as forklifts maneuvering within covered storage areas, stacking of goods in proximity to the sprinkler-bearing ceiling, etc.
Malicious activation of fire sprinklers is sometimes effected by hostile individuals, such as angry workers, hooligans or vandals, who seek out ways to cause damage. Occasionally, the fire-protected areas are situated within inherently violent and/or delinquent environments such as prisons, detention centers or correctional institutions, in which tampering is not an exceptional phenomenon.
The activation of fire sprinklers over the protected area causes severe water damage. Many kinds of stored merchandise are water sensitive, e.g. electronic equipment, books, etc. In some cases, the damage to stored materials may even be irreparable, as in the case of archives or museums.
The various requirements for automatic fire sprinklers are defined in the National Fire Protection Association (NFPA) 13 Standard for the Installation of Sprinkler Systems, which was also adopted by the American National Standards Institute (ANSI). Among these requirements, the NFPA 13 standard also includes the specific requirements for the various thermally sensitive elements, but there are no obligatory requirements concerning means for preventing accidental or malicious activation. Even so, there exist several prior art sprinklers having mechanisms for reducing the probability of accidental or malicious activation.
Most fire sprinkling systems belong to a type known in the art as the Wet-pipe system. This type of system is the easiest to design and install, and the simplest to maintain. Wet-pipe systems contain water under pressure at all times and utilize a series of closed sprinklers. When a fire occurs and produces a sufficient amount of heat to activate one or more sprinkler, because an automatic water supply is mandated, water immediately discharges from the open sprinklers. Wet-pipe systems are inherently reliable and relatively inexpensive to maintain.
However, a fire sprinkler for use in a Wet-pipe system is very vulnerable. The thermally sensitive element, which is exposed and mechanically-weak, can easily be tampered with or accidentally broken, such that the fire sprinkler is activated, causing water damage to the goods in the protected area.
One known system for overcoming this problem is the Pre-action system. In Pre-action systems, which are mentioned in the NFPA 13 standard, the piping is charged with air under pressure rather than water, while the water supply is held back by means of a pre-action valve.
The system is equipped with a supplemental detection system such as smoke detectors or heat sensitive detectors, which control the pre-action valve. Operation of the detection system allows the pre-action valve to automatically open and admit water into the piping network. Water will discharge from the system only if a fire has generated a sufficient quantity of heat to cause operation of one or more sprinklers. In essence, the system acts appears as a Wet-pipe system once the pre-action valve operates.
Because water is held back with a pre-action valve, water does not flow into the system until the supplemental fire detection system is activated, and the pre-action valve receives a signal to open. The pre-action valve remains in a closed position until the detection system is activated.
A variation of the standard or single-interlock Pre-action system is the double-interlock Pre-action system. In the double interlock system, water enters the system piping only when both the supplemental detection system and the sprinklers on the system operate. Another variation of a Pre-action system is the non-interlock system, in which either activation of the supplemental detection system or a sprinkler initiates water flow through the system.
One of the main disadvantages of Pre-action systems is a considerably longer reaction time to a heat stimulus (i.e., a real fire) with respect to conventional Wet-pipe systems. Water begins discharging only after a pre-action main valve opens after getting at least two independent indications from the sprinklers or from one valve and one additional indicator, and after the empty piping system is completely filled. The resulting, cumulative time lag enables a fire to further develop and cause even greater fire damage. Moreover, because of the longer reaction time, the required water supply for Pre-action systems, per area of coverage area, is about 30% higher than in Wet-pipe systems.
Moreover, Wet-pipe systems, not Pre-action systems, are the preferred fire protection system for archives and the like, because of the dangerous downside of the Pre-action systems, i.e., more extensive fire damage in the event of a fire. The risk of wet documents is considered to be less problematic than documents burned beyond recognition.
Another drawback of Pre-action systems is that malicious tampering can also damage the pre-action valve so as to effect a water discharge, or alternatively, the tampering may damage any of the additional indicators, causing parts of the system to be inoperative during a real fire emergency.
It should also be noted that relative to the simple Wet-pipe systems, Pre-action systems are much more expensive and are also complicated to install and maintain.
Another known, specialized activation system utilizes Institutional sprinklers, such as Viking® Model HQR-2, manufactured by The Viking Corporation, Mich., U.S.A., or Model TFP PH5, manufactured by Tyco® Fire Products, Pennsylvania, U.S.A.
Characteristically, Institutional sprinklers are designed and installed such that most of the operating parts of the sprinkler are concealed in a metal housing inside the ceiling, except for a threaded escutcheon plate protruding from the ceiling, and tightly attached thereto. The pipe leading to the sprinkler is anchored, and a special locking prevents the removal of the threaded escutcheon plate from the ceiling.
A deflector is held by a thermally sensitive element, both of which are concealed inside the escutcheon plate of the sprinkler, until being activated by the thermally sensitive element. The thermally sensitive element, which is made of a metal solder, melts when the rated temperature is reached, releasing the linkage mechanism that holds the sprinkler closed and allowing the deflector to extend so as to discharge and distribute water.
Although systems with Institutional sprinklers provide additional protection against both accidental and malicious activation, with respect to Wet-pipe systems, Institutional sprinklers are still prone, albeit to a lesser degree, to malicious activation. Moreover, Institutional sprinklers are much more costly than their Wet-pipe system counterparts, and are designed solely for light hazard occupancy needs.
There is therefore, a recognized need for, and it would be highly advantageous to have, a device for safely and reliably preventing accidental and malicious activation of automatic fire sprinklers, a device that is efficient and inexpensive, and does not compromise the reaction time in extinguishing genuine fire hazards.